Optical devices which change their optical states when electricity is supplied thereto have been proposed. For example, Patent Literature (PTL) 1 discloses a light-adjusting element in which an electrolyte layer including an electrochromic material that contains silver is sandwiched between a pair of transparent electrodes and depressions and protrusions of nanometer-scale order are provided in one of the transparent electrodes. The light-adjusting element in PTL 1 can form a mirror state through application of a voltage.